Constant velocity joints (CV joints) are common components in vehicles. Constant velocity joints are often employed where transmission of a constant velocity rotary motion is desired or required. CV joints are typically greased or otherwise lubricated for the life of the component. The joints are sealed to retain the grease or lubricant inside the joint while keeping contaminants and foreign matter, such as water and dirt, out of the joint. Moreover, a sealing boot, which may be made of rubber, thermoplastic, silicone material, or the like, usually encloses the internal components of the CV joints thus closing an open end. Additionally, a second open end may also be enclosed with an internal cover to close off the CV joint from the contaminants.
During operation, a CV joint may create excess internal pressure in the inner chamber of the joint. This is usually the result of temperature, which may be generated during operation. In such instances, it is often desirable to vent pressurized gases from the chamber of the joint to the outer atmosphere to reduce the internal temperature of the joint. The venting prevents undesirable pressure build-up during operation of the joint that could damage or compromise components such as the sealing boot. Consequently, many CV joints include a means for venting. An example of known venting means include a small hole in the center of the grease cap. However, this venting technique may allow an unwanted release of the grease or lubricant and/or the introduction of contaminants into the joint.
A joint may also be sealed without a vent valve or other vent. However, the relative pressure differences created within the boot and joint assembly by thermal cycling may deform the boot beyond a desirable amount, thereby resulting in premature boot failure.
One-way valves have been used to vent internal pressure within a CV joint. However, these valves may result in a negative pressure (a value that is undesirably less than atmospheric) when the joint cools, and may result in an unacceptable amount of stress within the boot, leading to a premature boot failure.
In traditional CV joint assemblies, a small end of the boot or neck is secured at a shaft-mating portion to the shaft to prevent any relative movement therebetween. Relative movement between the shaft-mating portion of the boot and the shaft may wear the boot and/or the shaft and may result in sufficient wear to permit grease to undesirably escape the joint chamber, or may permit contaminants to undesirably enter the joint chamber.
Thus, a joint may allow grease or other lubricants to undesirably leak from joint chamber while permitting undesired contaminants to enter during normal operations. What is needed, therefore, is a constant velocity joint that can accommodate the pressure changes within a joint chamber of a joint assembly while reducing or eliminating any loss of lubricants and introduction of contaminants.